The present invention relates to a post-tensioned pole system. In particular, the present invention relates to a post-tensioned pole system includes one or more precast segments which are coupled to one another by a connector and post-tensioned through the use of at least one strand that is external to the wall thickness of the pole segments.
It is well known that poles are used in a wide variety of applications including electrical transmission and distribution environments, lighting, telecommunications and as supports for wind energy turbines. When used in these environments, the poles are subjected to forces from the wind, water and structural loads such as the weight of wire transmission lines or a wind turbine. These forces create a moment or torque that the pole must resist in order to remain in an upright position. In resisting these forces, the pole has a tendency to flex thereby putting the bottom portion of the pole in compression and the top portion of the pole in tension.
In the past, the poles have been formed of various materials such as steel, wood, concrete, masonry materials and any combination thereof. The use of concrete to form the poles is relatively common due to its availability. However, the use of concrete to form the poles suffers from a number of drawbacks. For instance, while concrete is capable of withstanding a substantial amount of compression force, its ability to resist tension is considerably low. Therefore, different techniques have been established in an effort to enhance the concretes ability to withstand the tension forces imposed on the pole.
One technique used to enhance the ability of the concrete to withstand tension forces is pre-tensioning. Pre-tensioning the concrete has been accomplished by embedding strands within the concrete walls of the concrete using a spun or static cast technique. In the static cast method, the strands are arranged within the form prior to pouring the concrete. Both ends of each strand are jacked to place the strands in tension. The concrete is then placed into the form embedding the strands therein. The strands are cut after the concrete has gained adequate strength, releasing the force to the concrete. The tension in the strands places the concrete pole into compression thereby allowing it to withstand a greater amount of tension force. The spun cast technique is similar to the static method in that the strands are placed in the form prior to the addition of the concrete. However, instead of placing the concrete into a static form, the concrete is poured into a machine that spins the concrete forcing the concrete to the outer walls of the form and embedding the strands within the wall of the structure.
The aforementioned pre-tensioning techniques also suffer from a number of deficiencies. One problem with the spun cast method is that the concrete aggregate separates due to centrifugal force thereby making concrete weak and susceptible to cracking due to unequal distribution of aggregate. In addition, the equipment used to spin the concrete is expensive. In addition, both of the aforementioned methods of pre-tensioning concrete poles are problematic in that it takes a considerable amount of time to properly position the strands in the form prior to pouring the concrete.
Additionally, there other problems associated with current concrete pole structures. For example, the concrete structures that are used in these environments are typically unitary structures that extend to a height of about 80-90 feet. This is problematic because certain power transmission line applications may require the poles to extend to greater heights. Additionally, given the fact that poles are a unitary structure, it is very difficult to transport the pole structures from an off-site location to the construction site. Once the poles arrive at the site, they require large cranes and heavy machinery to lift them into position due to the weight and length of the pole.
Accordingly, there remains a need for a segmental post-tensioned pole system that increases maximum height of pole while reducing the difficulty in transporting the pole from off-site location to the construction site. In addition, there is also a need to simplify the installation and manufacture of the pole. The present invention fills these needs as well as various other needs.